Diamond tools

ABSTRACT

A method comprising: selecting a diamond material; irradiating the diamond material to increase toughness and/or wear resistance of the diamond material; and processing the diamond material into one or more diamond tool pieces, wherein the diamond material is selected from the group consisting of: a HPHT diamond material having a total equivalent isolated nitrogen concentration in the range 1 to 600 ppm; a CVD diamond material having a total equivalent isolated nitrogen concentration in the range 0.005 to 100 ppm; and a natural diamond material having a total nitrogen concentration in the range 1 to 2000 ppm, wherein the irradiating comprises controlling energy and dosage of irradiation to provide the diamond material with a plurality of isolated vacancy point defects, the isolated vacancy point defects having a concentration in a range 1×10 14  to 1×10 21  vacancies/cm −1

FIELD OF INVENTION

The present invention relates to diamond tools and methods of making thesame.

BACKGROUND OF INVENTION

For any application a user must consider a number of factors whenchoosing a tool material. Such factors including: cost; toughness; wearrate/hardness; ability to process a desired working surface such as acutting edge; useful lifetime; and inertness to chemical effects withthe material to be processed.

An ideal tool material is one which is both hard and tough. These twoproperties of materials used in wear and tear applications are oftenpresented on two perpendicular axes. Very simply, wear is a measurementof the amount of material removed per unit of operation. Toughness is ameasure of a material's resistance to crack propagation.

There is an ongoing desire to provide materials which are harder,tougher, stronger and more wear resistant. There is also an ongoingdesire to provide faster, more precise and cleaner production methodswhich add up to cost efficiency and improved performance. It is an aimof certain embodiments of the present invention to at least partiallyaddress some of these needs.

Diamond materials are the materials of choice for many premiumperformance cutting, drilling, grinding and polishing tools. Diamondmaterials are used in tooling solutions across a range of industriesincluding a variety of metal, stone and woodworking industries. Examplesinclude aerospace and automotive manufacturing, furniture production,stone quarrying, construction, mining and tunnelling, mineralprocessing, and the oil and gas industries.

Diamond's hardness properties make it the ultimate material in terms ofwear. However, diamond's limited ability to plastically deform understress at the tool's working temperature leads to more rapid crackpropagation in comparison to much tougher materials such as steel.

Previous attempts to improve the durability of diamond have involvedeither adapting the method of forming the diamond material or treatingthe diamond material after forming the material. For example, WO01/79583 teaches a process for improving the durability of adiamond-type tool to increase the impact strength and fracturetoughness. The process involves implanting ions into the surface of adiamond-type tool. Ion implantation is a materials engineering processby which ions of a material can be implanted into another solid, therebychanging the physical properties of the solid. Under typicalcircumstances ions are implanted to a depth in the range 10 nanometersto 1 micrometer. WO 01/79583 teaches ion implantation which penetrates adiamond surface to a depth in the range 0.02 μm to 0.2 μm. Preferredions include chromium, nickel, ruthenium, tantalum, titanium andyttrium.

U.S. Pat. No. 4,184,079 and GB 1588445 also teach a method fortoughening diamond by bombarding the diamond with ions of sufficientenergy to penetrate the diamond surface. Various ions are suggestedincluding carbon, nitrogen and hydrogen ions. It is described that theions form a dislocation network in the diamond crystal lattice therebyinhibiting microcleavage of the diamond. It is further described thatthe dislocations can be confined to a depth of from 10 nanometers to 1micrometer below the surface of the diamond crystals in order to form ahard skin on the surface thereof. It is taught that the dose of ionsshould be quite small, in the range 10¹⁶ to 10¹⁸ ions cm⁻², and haveenergies in the range 10 keV to 10 MeV, more preferably less than 100keV so that the species implanted by the bombardment do not have adetrimental effect on the diamond material. As ion bombardment ofdiamond results in the amorphisation and softening of the surface unlessthe temperature is held sufficiently high to maintain the crystalstructure, it is taught to use a temperature of at least 500° C. duringion bombardment.

GB 1588418 discloses a process for improving the wear characteristics ofindustrial diamonds. The process comprises implanting ions into thesurface of the diamond. Carbon and nitrogen ions are suggested for thispurpose.

U.S. Pat. No. 4,012,300 discloses a method of altering the friability ofabrasive particles, particularly diamond and cubic boron nitrideparticles, by subjecting the particles to irradiation. Proton, neutronsand gamma radiation are suggested with neutrons being preferred.

US2006065187 discloses a tough CVD diamond material which is grown in anatmosphere having a nitrogen to methane ratio of about 4% N₂/CH₄ atabout 1050° C.-1200° C. and then annealed.

US2009110626 teaches that nitrogen containing single crystal CVDdiamonds treated by a low pressure, high temperature annealing processhave a high toughness.

It is an aim of certain embodiments of the present invention to improvethe toughness and/or wear resistance of diamond tools. It is a furtheraim of certain embodiments of the present invention to avoid some of theproblems associated with the aforementioned methods.

SUMMARY OF INVENTION

According to one aspect of the present invention there is provided amethod comprising:

selecting a diamond material;

irradiating the diamond material to increase toughness and/or wearresistance of the diamond material; and

processing the diamond material into one or more diamond tool pieces,wherein the diamond material is selected from the group consisting of:

a HPHT diamond material having a total equivalent isolated nitrogenconcentration in the range 1 to 600 ppm;

a CVD diamond material having a total equivalent isolated nitrogenconcentration in the range 0.005 to 100 ppm; and

a natural diamond material having a total nitrogen concentration in therange 1 to 2000 ppm,

wherein the irradiating comprises controlling energy and dosage ofirradiation to provide the diamond material with a plurality of isolatedvacancy point defects, the isolated vacancy point defects having aconcentration in a range 1×10¹⁴ to 1×10²¹ vacancies/cm⁻³.

The present invention proposes that there is an interaction between themechanism by which irradiation increases toughness and/or wearresistance of diamond material and the mechanism by which nitrogenwithin the diamond crystal matrix increases toughness and/or wearresistance. Although this mechanism is not fully characterized, onepossibility is that irradiation introduces a relatively evendistribution of vacancy defects within the crystal matrix which can actas crack stops and/or introduce regions of stress/strain within thediamond crystal matrix which may act to inhibit crack propagation andincrease toughness. Nitrogen impurities within the crystal matrix mayfunction to trap vacancies introduced by the irradiation to form N—V—Nor N—V centres. During manufacture, and in use, a diamond tool piecebecomes hot. As such, vacancies introduced by irradiation may becomemobile within the crystal matrix. However, it is desirable to provide arelatively even distribution of vacancies within the crystal matrix toact as crack stops. As such, a relatively even distribution of vacanciesintroduced by irradiation may be maintained by ensuring that a suitableconcentration of nitrogen is present within the crystal matrix toprevent the vacancies migrating through the diamond crystal structure.The vacancy point defects may be in the neutral (V⁰) and negative chargestates (V). The total vacancy concentration ([V_(T)]=[V⁰]+[V]) may be inthe range: 1×10¹⁴ to 1×10²² vacancies/cm⁻³; 1×10¹⁴ to 1×10²¹vacancies/cm⁻³; 1×10¹⁴ to 1×10²⁰ vacancies/cm³; 1×10¹⁵ to 1×10²¹ cm⁻³;5×10¹⁵ to 1×10²⁰ vacancies/cm⁻³; 1×10¹⁵ to 1×10¹⁹ vacancies/cm³; 1×10¹⁵to 1×10¹⁸ vacancies/cm³; 1×10¹⁵ to 1×10¹⁷ vacancies/cm³; 1×10¹⁶ to5×10¹⁹ vacancies/cm⁻³; or 5×10¹⁶ to 1×10¹⁹ vacancies/cm⁻³ or 1×10¹⁶ to1×10¹⁷ vacancies/cm³.

In addition to the above, it has been recognized that CVD, HPHT, andnatural diamond are structurally different materials with, for example,different distributions of nitrogen. Natural diamond for example, tendsto have aggregated nitrogen defects (Type Ia) whereas synthetic CVD andHPHT diamond material tends to have isolated nitrogen defects (Type Ib).Materials having different types and distributions of nitrogen defectsbehave differently after being subjected to irradiation. Furthermore,the nitrogen content can affect other characteristics such as CVDdiamond growth. As such, the optimum amount of nitrogen required to bepresent in the diamond material to interact with vacancy defectsintroduced by irradiation will vary according to the type of diamondmaterial which is irradiated.

In light of the above, and in accordance with the present invention, itis proposed that for irradiated material, the optimum isolated nitrogenconcentration for HPHT diamond material lies in the range 1 to 600 ppm,the optimum isolated nitrogen concentration for CVD diamond materiallies in the range 0.005 to 100 ppm, and the optimum isolated nitrogenconcentration for natural diamond material lies in the range 1 to 2000ppm. Using such materials, the irradiation and the nitrogen act in acompatible manner to provide a tougher more wear resistant material.

The HPHT diamond material may have a total equivalent isolated nitrogenconcentration in the range 10 to 300 ppm, 10 to 200 ppm, 50 to 250 ppm,100 to 200 ppm, 10 to 100 ppm, or 10 to 50 ppm.

The CVD diamond material may have a total equivalent isolated nitrogenconcentration in the range 0.01 to 50 ppm, 0.05 to 20 ppm, 0.08 to 5ppm, or 0.1 to 2 ppm.

The natural diamond material may have a total nitrogen concentration inthe range 200 to 2000 ppm, 500 to 1500 ppm, 800 to 1300 ppm, or 1000 to1200 ppm.

It is to be noted that the nitrogen concentrations discussed above aremeasured as an average concentration over a majority volume of thediamond material. The majority volume may be greater than or equal to50%, 60%, 70%, 80%, or 90% of the total volume of the diamond material.This is to account for the fact that different diamond growth sectorshave different rates of nitrogen uptake leading to concentrationvariations.

The total equivalent isolated nitrogen concentration for a diamondmaterial can be measured by techniques known by persons skilled in theart, for example the concentration can be calculated by deconvolutingthe absorption spectrum of the one phonon part of the FTIR spectrum. Thetotal concentration of nitrogen including aggregated nitrogen may bedetermined using secondary ion mass spectroscopy (SIMS).

The irradiation may comprise electrons, neutrons, X-rays, gammaradiation, protons, or alpha particles.

The irradiation should be of sufficient energy to generate isolatedvacancies or relatively small cluster defects in the diamond materialwhich can act as crack stops. If the energy if the radiation isrelatively high or the radiation comprises relatively heavy particles,carbon atoms are knocked off their lattice sites with enough energy toknock further carbon atoms of their lattice sites resulting in what isknown as cascade damage. This results in clusters of defects and aregion of stress/strain within the diamond crystal matrix which may actto inhibit crack propagation and increase toughness. Small clusterdefects are acceptable. However, if the energy of the radiation is toohigh, the cascade damage becomes too extensive and toughness and/or wearresistance is reduced. Furthermore, if the energy of the radiation istoo low, the radiation does not penetrate sufficiently into the diamondmaterial to provide a bulk treatment of the diamond material.

In light of the above, it is advantageous to irradiate the diamondmaterial in order to form a large number of relatively evenly spacedisolated vacancies or small cluster defects without the individualclusters becoming too large in size. If cluster defects are formed, theyshould preferably have a maximum length no greater than 50 atoms, 20atoms; 10 atoms; or 5 atoms in length. The size of the cluster defectscan be measured using transmission electron microscopy (TEM) or positronannihilation techniques.

The energy of the radiation will depend on the type of radiation and themechanism of energy transfer between the radiation and a carbon atom ithits within the diamond crystal matrix. The dose of radiation will alsodepend on the type of radiation and the number of vacancies produced perparticle of radiation.

An iterative process can be used to find optimum vacancy defect levels.A diamond material can be irradiated, tested, re-irradiated, and so onto find the optimum defect levels for a particular diamond material fora particular type of tool piece and tool application.

According to certain embodiments, the irradiation is preferably above anenergy and dose rate which leads to a change in colour of the diamondmaterial. It is also advantageous that the irradiation is kept below anenergy and dose rate which would lead to amorphization of the diamondmaterial. Amorphization has a detrimental effect on the mechanicalproperties of the diamond material. In general, the longer theirradiation dose the more vacancy defects will be introduced. However,the rate of vacancy incorporation may vary according to the nature ofthe starting material.

For electrons, the irradiation may have an energy: 30 keV or greater; inthe range 0.1 MeV to 12 MeV; in the range 0.5 MeV to 10 MeV; in therange 1 MeV to 8 MeV; or in the range 4 MeV to 6 MeV. The dosage ofelectron irradiation may be: 1×10¹⁵ e⁻/cm² or greater; in the range1×10¹⁶ e⁻/cm² to 1×10¹⁹ e⁻/cm²; in the range 1×10¹⁷ e⁻/cm²to 1×10¹⁹e⁻/cm²; or in the range 2×10¹⁸ e⁻/cm²to 1×10¹⁹ e⁻/cm².

For neutrons, the irradiation may have an energy: in the range 1.0 keVto 12 MeV; in the range 1.0 keV to 10 MeV; in the range 100 keV to 8MeV; in the range 100 keV to 6 MeV; or in the range 500 keV to 4 MeV.The neutrons will tend to be distributed over a range of energies.Accordingly, at least 50%, at least 60%, at least 70%, or at least 80%of the neutrons fall within one of the aforementioned ranges. The dosageof neutron irradiation may be: 1×10¹⁴ neutrons/cm² or greater; in therange 1×10¹⁴ neutrons/cm² to 1×10¹⁸ neutrons/cm²; in the range 1×10¹⁵neutrons/cm² to 5×10¹⁷ neutrons/cm²; or in the range 1×10¹⁵neutrons/cm²to 1×10¹⁷ neutrons/cm².

For gamma rays, the irradiation may have an energy in the range 0.1 to12 MeV, 0.2 to 10 MeV, or 0.3 to 8 MeV. The dosage of gamma rayirradiation may be 5×10¹⁶ γ-ray/cm² or greater, in the range 1×10¹⁷ to5×10²¹ γ-ray/cm², or in the range 5×10¹⁷ to 1×10²¹ γ-ray/cm².

During irradiation according to certain embodiments of the presentinvention, the temperature of the diamond material is kept relativelylow. For example, the temperature may be: 500° C. or less; 400° C. orless; 300° C. or less; 200° C. or less; 100° C. or less; or 50° C. orless. In order to keep the temperature down, the diamond material may beactively cooled during irradiation. It is advantageous to keep thetemperature relatively low as an increase in temperature can result in adecrease in the number density of vacancy defects.

The method may also comprise the optional step of annealing the diamondmaterial in addition to treatment by irradiation. The annealing step maybe performed before, during or after the irradiation step, or anycombination thereof. In certain applications it may be preferred toperform an annealing step before irradiating as an annealing step afterirradiating can result in a decrease in vacancy defects. The annealingmay be performed at a temperature of 1600° C. or greater, 1800° C. orgreater, 2200° C. or greater, or 2400° C. or greater. Embodiments of thepresent invention may include a combination of irradiating and arelatively low temperature anneal, or a combination of irradiating and ahigh pressure high temperature anneal. Embodiments also envisage thepossibility of iterative doses of radiation and/or iterative annealing.That is, more than one annealing and/or irradiation step may beperformed. For example, the diamond material may be annealed, thenirradiated, and then annealed. Further alternating irradiation andannealing steps may also be performed. Alternatively, the diamondmaterial may not be exposed to any substantial annealing step, at leastafter irradiation. By substantial annealing step, we mean an annealingstep which substantially and measurably changes the properties of thematerial. Annealing below 1800° C. can be conducted in an inertatmosphere whereas annealing above 1800° C. may require stabilisingpressures, especially if a long anneal is performed. The annealing istypically conducted for 30 seconds up to 50 hours. By inert atmosphere,we mean an atmosphere under which the diamond will not significantlydegrade during annealing. Examples include Argon and Neon.

A relatively low temperature anneal may be advantageous for certainapplications. In use, the diamond material can get hot, and most methodsof mounting the diamond tool piece also include brazing at, for example,900° C. As such, a low temperature anneal can be useful to ensure aconsistent performance of the diamond tool pieces in use. For example, alow temperature anneal at a temperature of 1500° C. or less, 1300° C. orless, 1200° C. or less, 1100° C., or less, or approximately 1000° C. canbe useful for certain applications.

The irradiation may be performed before, during, or after processing toform one or more tool pieces. The processing may involve treating,grinding, cutting and/or shaping the diamond material to form one ormore diamond tool pieces, each tool piece having a working surface suchas a cutting blade. For example, the processing may comprise forming oneof: a wear part; a dresser; a wire drawing die; a gauge stone; and acutter. For example, a tool piece may comprise a cutting edge having alength greater than or equal to 0.5 mm, 1 mm, 1.5 mm, or 2 mm. Themethod may further comprise incorporating the one or more diamond toolpieces into one or more tools and the irradiating may be performedbefore, during, or after this incorporating step.

Irradiating the diamond material prior to incorporating the materialinto a tool is advantageous in that the increase in toughness and/orwear resistance as a result of the irradiation can reduce the likelihoodof the diamond material being damaged during the processing stepsinvolved in incorporating the diamond material into the tool.Furthermore, other components in the tool may be damaged by theradiation and this is avoided if the diamond material is irradiatedprior to the diamond material being incorporated into the tool. Forexample, it is know that irradiation can reduce the toughness ofmetallic materials such as steel. Further still, existing manufacturingprocesses for forming tools using diamond material do not need to bealtered in any way if the diamond is pre-treated prior to toolmanufacture.

On the other hand, irradiating the diamond material after the diamondmaterial has been incorporated into the tool has the advantage thatexisting diamond tools can be treated to increase their toughness and/orwear resistance. Further still, the irradiation can be directed toparticular portions of the diamond material within the tool where it isdesired to increase the toughness and/or wear resistance. This avoidsthe need to irradiate other portions of the diamond material which maynot be required to have an increased toughness and/or wear resistance inuse.

In addition to improving the toughness and/or wear resistance of thetool, an increase in toughness and/or hardness of the diamond can allowthe diamond material to be processed in different ways. For example, anincrease in toughness can allow the diamond material to be processed toa sharper edge for more precise cutting without the edge cracking orchipping during processing or in use.

The diamond material can be irradiated to a depth of 1 μm or greater, 10μm or greater, 100 μm or greater, 500 μm or greater or 1 mm or greater.The diamond material may be irradiated throughout a total thickness ofthe diamond material.

The diamond material may also be exposed to radiation on more than oneside of the material. For example, a diamond plate may be exposed onboth main faces to achieve an even exposure of radiation. Similarly, aplurality of small particles may be shaken during irradiation such thatthe particles roll and receive a reasonably even exposure to theradiation over their surface. Rotation of the sample during irradiation,or repeated rotation followed by irradiation, can assist in achievingirradiation throughout the volume of diamond material and/or assist inachieving a relatively even distribution of vacancy defects.

An advantage of certain embodiments of the present invention over priorart ion implantation methods is that embodiments of the presentinvention can be more cost effective. This is because certainembodiments provide a bulk treatment of the diamond material rather thanjust a surface treatment. Accordingly, the irradiation can be donebefore processing the diamond material into a tool piece andincorporating the tool piece into a tool. Furthermore, bulk treatmentcan be applied to a large volume of material pieces with relativelysimple handling requirements. For example, diamond pieces do not need tobe carefully mounted in a certain orientation as is required for manysurface treatments. In contrast, prior art ion implantation methods needto be performed after processing of the diamond material. This isbecause prior art ion implantation methods generally result in anincrease in toughness only near the surface of the diamond material.Processing of the material into a tool piece by, for example, cutting,shaping and/or grinding the diamond material will remove the treatedsurface of such materials. Another advantage of certain embodiments ofthe present invention is that the tool pieces can be re-worked withouthaving to re-treat the tool pieces. A further advantage is thatirradiation prior to processing to form a tool piece can improve theworking surface achievable by the processing. For example, an irradiateddiamond material with increased toughness can be processed to a sharpercutting edge for more precise cutting without chipping or cracking thecutting edge during processing.

The diamond material according to embodiments of the invention may benatural diamond or synthetic diamond. The synthetic diamond may beformed by a high pressure high temperature (HPHT) method or by achemical vapour deposition (CVD) method. The diamond material could besingle crystal, polycrystalline, grit, diamond-like-carbon (DLC), or acomposite diamond material such as diamond grains dispersed in a metalmatrix (usually cobalt and known as PCD) or an inorganic matrix (such assilicon carbide and known as skeleton cemented diamond or ScD). Thediamond material may comprise crystals having a size: 1 nm or greater;100 nm or greater; 500 nm or greater; 1 micrometer or greater; 5micrometer or greater; 0.5 mm or greater; 1 mm or greater; 3 mm orgreater; or 10 mm or greater. The diamond material may comprise one ormore crystals and may form a body having at least one dimension up to,for example, 200 mm or more (for example, in a polycrystalline diamondplate or dome). The invention is particularly suited for application toHPHT and CVD diamond. However, certain embodiments may also be appliedto natural diamond.

Certain embodiments of the present invention propose to use neutronirradiation for increasing the toughness and/or wear resistance ofdiamond tool pieces having at least one dimension of 1 mm or greater,1.5 mm or greater, or 2 mm or greater. U.S. Pat. No. 4,012,300 describesa method of decreasing the friability (increasing the friability index)of natural diamond grit of 120/140 U.S. mesh (approximately 0.1 mmmaximum particle diameter) or 30/40 U.S. mesh (approximately 0.5 mmmaximum particle diameter) by irradiating the grit, in particular withneutrons. According to Zhou et al (Zhou, Y., Takahashi, T., Quesnel, D.J., Funknebusch, P. D., ‘Friability and Crushing Strength ofMicrometer-Size Diamond Abrasives Used in Microgrinding of OpticalGlass’, Metallurgical and Materials Transactions A, 27A (1996),1047-1053), friability is a measure of the crushing strength of materialwhen in the form of particulates under compressive impact loadingconditions. In contrast to U.S. Pat. No. 4,012,300 which teaches the useof neutron irradiation for decreasing the friability of small diamondparticles, certain embodiments of the present invention propose to useirradiation for increasing the toughness and/or wear resistance oflarger diamond tool pieces. It has been found that radiation can form asuitable distribution of defects of the correct size throughout arelatively large piece of diamond material in order to increase thetoughness and/or wear resistance of a diamond tool piece. This isneither disclosed nor suggested in U.S. Pat. No. 4,012,300.

According to certain embodiments of the present invention the diamondmaterial may be Type Ia, Type Ib, or Type IIa.

Preferably, the irradiation increases the useful lifetime of the diamondtool piece by 10% or greater, preferably 20% or greater, more preferably50% or greater of the lifetime of an untreated diamond tool piece.

In addition to increasing the toughness and/or wear resistance ofdiamond tools, the irradiation treatment of embodiments of the presentinvention has the bonus effect of producing diamond tool pieces withmore desirable colours. A tool of a specific colour is useful as thecolour also relates to its performance, thus giving the tools of thepresent invention a distinctive colour branding in addition toperformance advantages. Traditionally, synthetic diamond tool pieceshave generally contained diamond material which is yellow in colour.Particularly good results have been obtained by starting with a yellow,most preferably deep yellow, diamond material and irradiating the yellowdiamond material in order to increase toughness and/or wear resistance.The irradiation can also change the colour of the yellow diamondmaterial. A range of colours may be achieved depending on the exact typeof starting material, the type of radiation, and whether an annealingstep is performed in addition to irradiation. For example, colourless ornear colourless CVD diamond may turn blue or yellowish-green whenirradiated in accordance with an embodiment of the present invention. Ifirradiated and then heated to a temperature greater than approximately700° C. then the CVD diamond which was originally colourless or nearcolourless may turn colourless, orange, brown or a pink colour dependanton irradiation and annealing treatment. In contrast, yellow HPHT Type Ibdiamond may turn green when irradiated (depending on dose) in accordancewith an embodiment of the present invention. If irradiated and thenheated to a temperature greater than approximately 700° C. then theyellow HPHT Type Ib diamond may turn a red or purple colour (dependingon irradiation and anneal). In certain cutting application, the greendiamond obtained by irradiating HPHT Type Ib diamond has been found togive particularly good results.

Further still, the colour of diamond material according to certainembodiments of the present invention can change, for example, when acertain temperature is exceeded for a certain length of time. Thiscolour change can be used as a quality control indicator and/or anindicator that a diamond tool piece requires replacement. For example, agreen HPHT Type Ib diamond tool piece according to one embodiment of thepresent invention may turn red/purple after prolonged use at hightemperatures. This can act as an indicator that the diamond tool piecerequires replacement and/or if there is excessive heating due tomanufacturing issues, e.g. with the mounting or tool design andtherefore excessive heating is occurring.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention and to show how thesame may be carried into effect, embodiments of the present inventionwill now be described by way of example only with reference to theaccompanying drawings, in which:

FIG. 1 illustrates the basic steps involved in performing a methodaccording to an embodiment of the present invention;

FIG. 2 illustrates the basic steps involved in performing a methodaccording to another embodiment of the present invention; and

FIG. 3 illustrates the basic steps involved in performing a methodaccording to another embodiment of the present invention.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

FIG. 1 illustrates the basic steps involved in performing a methodaccording to an embodiment of the present invention. A diamond material10 is irradiated to form a diamond material 12 with increased toughnessand/or wear resistance. The diamond material 12 is then cut, for exampleusing a laser or mechanical cutter, to form one or more diamond toolpieces 14. One or more diamond tool pieces 14 are then brazed to acarrier 16 to form a diamond tool.

FIG. 2 illustrates the basic steps involved in performing a methodaccording to another embodiment of the present invention. A diamondmaterial 20 is cut, for example using a laser or mechanical cutter, toform one or more diamond tool pieces 22. The one or more diamond toolpieces 22 are then irradiated to form irradiated diamond tool pieces 24.One or more irradiated diamond tool pieces 24 are then brazed to acarrier 26 to form a diamond tool.

FIG. 3 illustrates the basic steps involved in performing a methodaccording to another embodiment of the present invention. A diamondmaterial 30 is cut, for example using a laser or mechanical cutter, toform one or more diamond tool pieces 32. One or more diamond tool pieces32 are then brazed to a carrier 34 to form a diamond tool. The one ormore diamond tool pieces 34 are then irradiated to form irradiateddiamond tool pieces 36.

The described embodiments of the present invention provide a method ofincreasing toughness and/or wear resistance of a tool comprising diamondmaterial, the method comprising irradiating the diamond material toincrease toughness and/or wear resistance. The irradiation treatmentsform vacancy defects in the diamond material which can be trapped bynitrogen within the diamond matrix.

The diamond material used in embodiments of the present invention may benatural diamond, HPHT diamond and CVD diamond. It will be understoodthat natural diamond, HPHT diamond and CVD diamond have their owndistinctive structural and functional characteristics and thus the terms“natural”, “HPHT” and “CVD” not only refer to the method of formation ofthe diamond material but also refer to specific structural andfunctional characteristics of the materials themselves. For example, asynthetic CVD diamond material may be unequivocally distinguished from asynthetic diamond material synthesized using HPHT techniques by thedislocation structure. In synthetic CVD diamond, dislocations generallythread in a direction that is roughly perpendicular to the initialgrowth surface of the substrate, i.e. where the substrate is a {001}substrate, the dislocations are approximately aligned parallel to the[001] direction. This is not true for synthetic diamond materialsynthesized using HPHT techniques. Thus the two types of material can bedistinguished by their different dislocation structures observed, forexample, in an X-ray topograph.

The diamond material used in embodiments of the present invention may beType Ia, Type Ib, of Type IIa. Type Ia and Type Ib diamonds containnitrogen. Although Type IIa diamonds are usually defined as containingno nitrogen, in practice they can contain low concentrations ofnitrogen. In Type Ia, the nitrogen atoms form various types of aggregatedefect whereas in Type Ib diamonds, the nitrogen atoms tend to beisolated as single impurities. Type Ia diamonds can be colourless,brown, pink, and violet. Natural Type Ib diamonds can be deep yellow(“canary”), orange, brown or greenish. The colour of a diamond isdetermined by the number, type and distribution of defects within thecrystal structure. Crystal defects include dislocations, microcracks,twin boundaries, point defects, and low angle boundaries. As such, forexample, the colour of diamond will depend on the type and distributionof impurities such as nitrogen as well as the type and distribution ofother defects such as dislocations. There is a large number of differenttypes and subclasses of defects within diamond. For example, there arenumerous different types of nitrogen defect alone, each having its ownspectral characteristics.

The tools formed by embodiments of the present invention may be used fora range of applications including cutting, grinding, polishing, drillingand/or wire drawing. Particularly good results have been obtained todate for cutting applications and wire drawing.

The diamond material in the tool may be configured into a number ofpossible crystallographic orientations including 2-point, 3-point and4-point crystals which correspond to {110}, {111} and {100}crystallographic planes respectively. Particularly good results havebeen obtained for 3-point HPHT Type Ib diamond in a wire drawing tooland 2-point HPHT Type Ib diamond in a cutting tool. Optionally, theworking surface of the diamond tool piece is formed by a single sectorof diamond material.

EXAMPLES Electron Irradiation

Electron irradiation (for example, using electrons with energies lessthan or equal to 12 MeV) typically introduces vacancies in an isolatedform. These may be in the neutral (V⁰) and negative charge states (V).The total vacancy concentration ([V_(T)]=[V⁰]+[V]) post irradiationshould preferably be in the range: 1×10¹⁴ to 1×10²¹ vacancies/cm³;1×10¹⁵ to 1×10²¹ vacancies/cm³; 5×10¹⁵ to 1×10²⁰ vacancies/cm³; 1×10¹⁶to 5×10¹⁹ vacancies/cm³; or 5×10¹⁶ to 1×10¹⁹ vacancies/cm³. Such aconcentration of defects can be formed, for example, using electronirradiation having a dose rate: 1×10¹⁵ e⁻/cm² or greater; in the range1×10¹⁶ e⁻/cm² to 1×10¹⁹ e⁻/cm²; in the range 1×10¹⁷ e⁻/cm²to 1×10¹⁹e⁻/cm²; or in the range 2×10¹⁷ e⁻/ cm² to 1×10¹⁹ e⁻/cm².

The electron irradiation may have an energy of: 30 keV or greater; inthe range 0.1 MeV to 12 MeV; in the range 0.5 MeV to 10 MeV; or in therange 1 MeV to 8 MeV. The preferred energy is that which introduces anear uniform concentration of vacancies in a nitrogen doped diamond,while minimizing the formation of cascade damage e.g. vacancy chains.For the results reported here it was found that 4.5 MeV provided a goodcompromise between these two factors.

Factors such as diamond temperature, beam energy, beam flux, and eventhe starting diamond's properties can affect the [V_(T)] produced for afixed experimental irradiation set-up and time. Irradiation is typicallycarried out with the sample mounted under ambient conditions ˜300 K withonly minimal temperature rise during the irradiation dose (e.g. lessthan 100 K). However, factors such as beam energy and beam flux can leadto sample heating. Preferably the sample is held as cold as possible(with even cryogenic cooling at 77 K being advantageous under somecircumstances) to enable high dose rates without compromisingtemperature control and thus minimize the irradiation time. This isadvantageous for commercial reasons.

The vacancy concentration can be measured spectroscopically. Forexample, to measure concentrations of isolated vacancies, spectra areobtained at 77 K, using liquid nitrogen to cool the samples, since atthat temperature sharp peaks at 741 nm and 394 nm are seen that areattributable to neutral and negatively charged isolated vacanciesrespectively. The coefficients that are used for the calculations ofconcentrations of isolated vacancies in the present specification arethose set out by G. Davies in Physica B 273-274 (1999) 15-23, asdetailed in Table 1 below. In Table 1, “A” is the integrated absorption(meV cm⁻¹) in the zero phonon line of the transition, measured at 77 K,with the absorption coefficient in cm⁻¹ and the photon energy in meV.The concentration is in cm⁻³.

TABLE 1 Defect Calibration V⁻ A_(ND1) = (4.8 ± 0.2) × 10⁻¹⁶[V⁻] V⁰A_(GR1) = (1.2 ± 0.3) × 10⁻¹⁶[V⁰]

According to one arrangement, a yellow Type Ib HPHT synthetic diamondwas irradiated with electrons. The electron irradiation was carried outat 4.5 MeV, 20 mA at 50% scan width for 2 hrs using an instrument suchas that found at Isotron plc. The overall dose provided to the samplewas 1.95×10¹⁸ e⁻/cm². The diamond material turned green in colour. Nosubstantial annealing step was performed although the material wassubjected to a short heating step when the material was brazed to acarrier to form a tool.

The irradiated diamond material was tested in cutting applications andwire drawing applications. Cutting tests showed that the irradiateddiamond out performed natural stones and was far better than any other2-point or 4-point stone of either synthetic or natural diamond. Wiredrawing tests also showed improved performance for the irradiatedmaterial. The irradiated diamond material degraded much more slowly thanstandard synthetic diamond in use. Furthermore, lines and scratcheswhich are sometimes formed in synthetic or natural diamond materials inuse were not observed in the irradiated material.

Trials have also been completed on four irradiated 2-point HPHT diamondtools in a fly cutting application. The electron irradiation was carriedout at 4.5 MeV, 20 mA at 50% scan width for 2 hrs using an instrumentsuch as that found at Isotron plc, the overall dose provided the samplewas 1.95×10¹⁸ e⁻/cm². The tool pieces were mounted onto a standardtungsten carbide shank using a standard braze (2-3 mins at 900° C.).They were used in a fly cutting application, processing copper andaluminium for metal optics applications such as CO₂ laser mirrors. Suchinterrupted cutting is a particularly good test as there is repeatedimpact on the tool pieces. There was an approximately 50% improvement inthe tool lifetime of the irradiated HPHT tool pieces compared tountreated HPHT diamond.

According to another arrangement, a colourless or near colourless singlecrystal CVD diamond plate was irradiated with electrons to form a bluematerial. This material can be used, for example, to form a cuttingblade. The cutting blade can be cut out of a blank plate using, forexample, a laser. The blue material can be optionally annealed atapproximately 700° C. to form an orange/light brown material.

Neutron Irradiation

Neutron irradiation tends to knock carbon atoms off their lattice siteswith enough energy to knock further carbon atoms of their lattice sitesresulting in what is known as cascade damage. This results in clustersof defects and a region of stress/strain within the diamond crystalmatrix which may act to inhibit crack propagation and increasetoughness. If the energy of the neutrons is too high, the cascade damagebecomes too extensive and toughness and/or wear resistance is reduced.

In light of the above, it is advantageous to irradiate the diamondmaterial in order to form a large number of isolated and/or relativelysmall cluster defects without the individual clusters becoming too largein size. It has been found that a suitable size of cluster defects canbe formed using neutron radiation having an energy: in the range 1.0 keVto 12 MeV; in the range 1.0 keV to 10 MeV; in the range 100 keV to 8MeV; in the range 100 keV to 6 MeV; or in the range 500 keV to 4 MeV.The neutrons will tend to be distributed over a range of energies.Accordingly, at least 50%, at least 60%, at least 70%, or at least 80%of the neutrons fall within one of the aforementioned ranges.

Neutron irradiation according to the present invention can introduce anear uniform concentration of isolated vacancies and/or small clusterdefects, while minimizing the formation of extensive cascade damage e.g.long vacancy chains. It is difficult to measure the concentration ofcluster defects. However, the concentration of isolated defects can bereadily characterized spectroscopically. Vacancy point defects may be inthe neutral (V⁰) and negative charge states (V). The total isolatedvacancy concentration ([V_(T)]=[V⁰]+[V]) may be in the range: 1×10¹⁴ to1×10²⁰ vacancies/cm³; 1×10¹⁵ to 1×10¹⁹ vacancies/cm³; 1×10¹⁵ to 1×10¹⁸vacancies/cm³; 1×10¹⁵ to 1×10¹⁷ vacancies/cm³; or 1×10¹⁶ to 1×10¹⁷vacancies/cm³. The presence of cluster defects can be detected by abroadening of the absorption peak for isolated vacancies. Such aconcentration of vacancy defects can be formed, for example, usingneutron irradiation having a dose rate: 1×10¹⁴ neutrons/cm² or greater;in the range 1×10¹⁴ neutrons/cm² to 1×10¹⁸ neutrons/cm²; in the range1×10¹⁵ neutrons/cm² to 5×10¹⁷ neutrons/cm²; or in the range 1×10¹⁵neutrons/cm² to 1×10¹⁷ neutrons/cm².

Embodiments of the present invention envisage the possibility of forminga large number of evenly spread isolated vacancies and/or relativelysmall cluster defects using neutron irradiation, while avoiding largeextensive cluster defects formed by extensive cascade damage as a resultof neutrons which are too high in energy. This requires the carefulselection of a neutron flux of an appropriate energy. It is advantageousto select an energy which results in cluster defects having a maximumsize limitation for individual clusters. This is consistent with theunderstanding that it is desirable to form relatively small, relativelyevenly spread defect clusters rather than large sprawling regions ofcascade damage. Accordingly, it is preferable that each of a pluralityof cluster defects has a maximum size no greater than 50 atoms inlength, more preferably no greater than 20 atoms in length, morepreferably still no greater than 10 atoms in length, and most preferablyno greater than 5 atoms in length. The size of the cluster defects canbe measured using transmission electron microscopy (TEM) or positronannihilation techniques.

As previously described, it is advantageous to keep the temperature ofthe diamond material relatively low during irradiation as an increase intemperature can result in a decrease in the number density of defects.One advantage of neutron irradiation is that it tends not to raise thetemperature of the diamond material as much as, for example, electronirradiation. As such, according to certain embodiments of the presentinvention no active cooling is required.

Another advantage of neutron irradiation is that the diamond materialdoes not usually need to be rotated during neutron irradiation toachieve a relatively even distribution of defects. In fact, oneadvantage of neutron irradiation over, for example, electron irradiationis that neutrons tend to penetrate more easily through an entire sampleto obtain a relatively even distribution of defects without rotation ofthe sample. It can thus be easier to achieve a high dose of radiationthrough a sample of diamond in a commercially viable way.

Care needs to be taken when selecting the diamond material to be neutronirradiated so that samples do not remain radioactive for an unreasonablylong period of time post irradiation. It is therefore necessary toensure the diamond material selected for neutron irradiation containssubstantially no metallic or other inclusions which will remainradioactive for an unreasonable length of time after exposure to neutronirradiation. In this regard, the diamond material may only be releasedpost neutron irradiation if the radioactivity is less than 4 Bq/g. Thediamond material selected for neutron irradiation should thereforepreferably contain no metallic inclusions having a size equal to or less10 μm, 5 μm, or 1 μm. The metallic inclusions should preferably be equalto or less than 0.1%, 0.01%, 0.001%, or 0.0001% of the total mass of thediamond. The diamond material should also preferably be acid cleanedimmediately before irradiation to remove any potentially radioactivespecies from the surface, thereby ensuring that the level ofradioactivity falls below 4 Bq/g after being held to ‘cool’ for equal toor less than 6 months, 4 months, 2 months, 1 month, 2 weeks, or 1 week.

Several CVD diamond samples have been irradiated with neutrons(typically containing approximately 0.1-0.5 ppm N). Imperial College'sUr²³⁵ Consort reactor at Silwood Park, Ascot, UK was used for thesetreatments (this reactor has now been decommissioned—an alternative canbe that found at Delft University, Holland.) The diamond material wastypically irradiated for between 14 and 28 hours, with an energydistribution within the reactor which peaked at 1 MeV, 59% of theneutrons falling into the energy range of 0.2 to 2.2 MeV and 86% ofneutrons falling into the energy range 0.2 to 12 MeV.

The diamond samples therefore received a dose of approximately 5×10¹⁵ to1×10¹⁶ neutrons/cm². A colour change was observed from colourless toyellow-green as a result of the neutron irradiation. Using coldUV-Visible spectroscopic measurements (using the same method ofcalculation as described above) the concentration of isolated neutralvacancies was measured to be in the range of 0.2-0.51 ppm (2×10¹⁶ to5.1×10¹⁶ vacancies/cm³). There was a clear broadening of the GR1 peakcompared to corresponding electron irradiated samples, which showsevidence for the formation of vacancy clusters in addition to isolatedvacancies.

The resulting material can be used, for example, to form a cuttingblade. The cutting blade can be cut out of a blank plate using, forexample, a laser. The irradiated material can be optionally annealed atapproximately 700° C.

Gamma Irradiation

Gamma rays can also be used to form vacancy defects within a diamondmaterial. For Gamma radiation, the irradiation may have an energy in therange 0.1 to 12 MeV, 0.2 to 10 MeV, or 0.3 to 8 MeV. The dosage of gammaray irradiation may be 5×10¹⁶ γ-ray/cm² or greater, in the range 1×10¹⁷to 5×10²¹ γ-ray/cm², or in the range 5×10¹⁷ to 1×10²¹ γ-ray/cm². Again,nitrogen impurities can be used to optimize the affect of introducingvacancies on the toughness and/or wear resistance of the diamondmaterial.

While this invention has been particularly shown and described withreference to preferred embodiments, it will be understood to thoseskilled in the art that various changes in form and detail may be madewithout departing from the scope of the invention as defined by theappendant claims.

1. A method comprising: selecting a diamond material; irradiating thediamond material to increase toughness and/or wear resistance of thediamond material; and processing the diamond material into one or morediamond tool pieces, wherein the diamond material is selected from thegroup consisting of: a HPHT diamond material having a total equivalentisolated nitrogen concentration in the range 1 to 600 ppm; a CVD diamondmaterial having a total equivalent isolated nitrogen concentration inthe range 0.005 to 100 ppm; and a natural diamond material having atotal nitrogen concentration in the range 1 to 2000 ppm, and wherein theirradiating comprises controlling energy and dosage of irradiation toprovide the diamond material with a plurality of isolated vacancy pointdefects, the isolated vacancy point defects having a concentration in arange 1×10¹⁴ to 1×10²¹ vacancies/cm⁻³.
 2. A method according to claim 1,wherein the HPHT diamond material has a total equivalent isolatednitrogen concentration in the range 10 to 300 ppm, 10 to 200 ppm, 50 to250 ppm, 100 to 200 ppm, 10 to 100 ppm, or 10 to 50 ppm.
 3. A methodaccording to claim 1, wherein the CVD diamond material has a totalequivalent isolated nitrogen concentration in the range 0.01 to 50 ppm,0.05 to 20 ppm, 0.08 to 5 ppm, or 0.1 to 2 ppm.
 4. A method according toclaim 1, wherein the natural diamond material has a total nitrogenconcentration in the range 200 to 2000 ppm, 500 to 1500 ppm, 800 to 1300ppm, or 1000 to 1200 ppm.
 5. A method according to claim 1, wherein theirradiating comprises irradiating with electrons, neutrons, X-rays,gamma rays, protons, or alpha particles.
 6. A method according to claim1, wherein the irradiating comprises radiation which has sufficientenergy to generate isolated vacancies or small cluster defects having amaximum length no greater than 50 atoms.
 7. A method according to claim6, wherein the irradiating introduces a plurality of cluster defectsinto the diamond material, each cluster defect having a maximum lengthno greater than: 20 atoms; 10 atoms; or 5 atoms in length.
 8. A methodaccording to claim 1, wherein the irradiating comprises irradiationbelow an energy and dose rate which would lead to amorphization of thediamond material.
 9. A method according to claim 1, wherein theirradiating comprises irradiating the diamond material above an energyand dose rate which leads to a change in colour of the diamond material.10. A method according to claim 1, wherein the irradiating is performedbefore, during, or after the processing.
 11. A method according to claim1, wherein the selecting comprises selecting one or more of a naturaldiamond material, a synthetic diamond material, a high pressure hightemperature (HPHT) diamond material, a chemical vapour deposition (CVD)diamond material, a single crystalline diamond material, apolycrystalline diamond material, a diamond-like-carbon material, adiamond, a Type Ib diamond material, and a composite diamond material.12. A method according to claim 1, wherein the irradiating comprisesirradiating the diamond material to a depth of: 1 μm or greater; 10 μmor greater; 100 μm or greater; 500 μm or greater; 1 mm or greater; orthroughout a total thickness of the diamond material.
 13. A methodaccording to claim 1, wherein the irradiating is performed at atemperature of: 500° C. or less; 400° C. or less; 300° C. or less; 200°C. or less; 100° C. or less; or 50° C. or less.
 14. A method accordingto claim 1, further comprising: cooling the diamond material during theirradiating.
 15. A method according to claim 1, further comprising:annealing the diamond material.
 16. A method according to claim 15,wherein the annealing is performed before, during or after theirradiating.
 17. A method according to claim 15, wherein the annealingis performed at a temperature: 1600° C. or greater; 1800° C. or greater;2200° C. or greater; or 2400° C. or greater.
 18. A method according toclaim 1, wherein the diamond material is not exposed to a substantialannealing step.
 19. A method according to claim 1, wherein theirradiating comprises one of: rotating the diamond material duringirradiation; or irradiating the diamond material, rotating the diamondmaterial, and irradiating the diamond material.
 20. A method accordingto claim 1, wherein the processing comprises shaping the diamondmaterial to form a working surface.
 21. A method according to claim 1,wherein the processing comprises forming one of: a wear part; a dresser;a wire drawing die; a gauge stone; and a cutter.
 22. A method accordingto claim 1, further comprising: incorporating the one or more diamondtool pieces into one or more tools.
 23. A method according to claim 22,wherein the irradiating is performed before, during, or after theincorporating.
 24. A method according to claim 1, wherein the vacancypoint defects have a concentration in the range: 1×10¹⁴ to 1×10²¹vacancies/cm³; 1×10¹⁵ to 1×10²¹ vacancies/cm³; 5×10¹⁵ to 1×10²⁰vacancies/cm³; 1×10¹⁶ to 5×10¹⁹ vacancies/cm³; or 5×10¹⁶ to 1×10¹⁹vacancies/cm³.
 25. A tool piece comprising diamond material irradiatedto increase toughness and/or wear resistance of the diamond material,wherein the diamond material is selected from the group consisting of: aHPHT diamond material having a total equivalent isolated nitrogenconcentration in the range 1 to 600 ppm; a CVD diamond material having atotal equivalent isolated nitrogen concentration in the range 0.005 to100 ppm; and a natural diamond material having a total nitrogenconcentration in the range 1 to 2000 ppm, wherein the diamond materialcomprises isolated vacancy point defects having a concentration in arange 1×10¹⁴ to 1×10²¹ vacancies/cm⁻³.
 26. A tool piece according toclaim 25, wherein the HPHT diamond material has a total equivalentisolated nitrogen concentration in the range 10 to 300 ppm, 10 to 200ppm, 50 to 250 ppm, 100 to 200 ppm, 10 to 100 ppm, or 10 to 50 ppm. 27.A tool piece according to claim 25, wherein the CVD diamond material hasa total equivalent isolated nitrogen concentration in the range 0.01 to50 ppm, 0.05 to 20 ppm, 0.08 to 5 ppm, or 0.1 to 2 ppm.
 28. A tool pieceaccording to claim 25, wherein the natural diamond material has a totalnitrogen concentration in the range 200 to 2000 ppm, 500 to 1500 ppm,800 to 1300 ppm, or 1000 to 1200 ppm.
 29. A tool piece according toclaim 25, wherein the diamond material comprises a plurality of vacancypoint defects, the vacancy point defects having a concentration in therange: 1×10¹⁵ to 1×10²¹ vacancies/cm³; 5×10¹⁵ to 1×10²⁰ vacancies/cm³;1×10¹⁶ to 5×10¹⁹ vacancies/cm³; or 5×10¹⁶ to 1×10¹⁹ vacancies/cm³.
 30. Atool piece according to claim 25, wherein the diamond material comprisesa plurality of cluster defects, the cluster defects having aconcentration in the range: 1×10¹⁴ to 1×10²¹ clusters/cm³; 1×10¹⁵ to1×10²¹ clusters/cm³; 5×10¹⁵ to 1×10²⁰ clusters/cm³; 1×10¹⁶ to 5×10¹⁹clusters/cm³; or 5×10¹⁶ to 1×10¹⁹ clusters/cm³.
 31. A tool pieceaccording to claim 25, wherein the diamond material comprises aplurality of cluster defects, each cluster defect having a maximumlength no greater than: 50 atoms; 20 atoms; 10 atoms; or 5 atoms inlength.
 32. A tool piece according to claim 25, where in the diamondmaterial is blue, orange, brown, green, red, purple, or black.
 33. Atool piece according to claim 25, where in the diamond material isconfigured to change colour in use indicating that the tool piecerequires replacement and/or there is excessive heating.
 34. A tool pieceaccording to claim 25, where in the tool piece is one of: a wear part; adresser; a wire drawing die; a gauge stone; and a cutter.
 35. A toolpiece manufactured using a method according to claim
 1. 36. A toolcomprising one or more tool pieces according to claim
 25. 37. (canceled)